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Discussion Starter #1
Hello,
I have a 1970 mustang with a 351c as my daily driver. Over the past couple of weeks a strange problem has started to occur. It is hard to explain but after running it for more than 20 minutes, sometimes less, it makes a weird hissing noise after I shut it off. White smoke then follows coming out of the air cleaner assembly. The smoke usually stops after 10 seconds. I live in Florida so it's constantly being driven in 90+ degree weather. Any suggestions as to what might be causing this?
Thanks,

Caleb
 

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Discussion Starter #3
I'll go double check but it hasn't seemed to be decreasing at a fast rate. I don't have an overflow tank so I have to put a little in every 2 months or so.
 

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Caleb,
Do you have a separator between the carb and intake? (reduces heat transfer)
BTW, if the coolant level is fine, should not adding coolant. If it's coming out of the overflow, then, check/replace the rad cap with one commensurate with your engine. Might consider a coolant recovery system to prevent any loss of coolant. Will need a cap to match.
 

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I bet you are flooding after shutdown. The hissing is the gas sizzling as it drops into the warm intake same with the white smoke.

I have found I need to run Gumout or something similar in my Holley regularly or I get inexplicable carb problems like that.
 

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I bet you are flooding after shutdown. The hissing is the gas sizzling as it drops into the warm intake same with the white smoke.

I have found I need to run Gumout or something similar in my Holley regularly or I get inexplicable carb problems like that.
Likely is heat soak. This is a spike in block temps after shut down with no coolant circulation. Reducing operating temp (check cooling and radiator efficiencies ) and or adding a phonic heat separator will help.
 

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What is your temp. gauge telling you? Keep in mind the factory temp. gauge is not that reliable after 40 years! I ruined a 351C because I had no idea it was overheating on the hwy. Sounds like fuel dripping out of carb. 351C has a dry intake...no coolant in that area.
 

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Discussion Starter #9
What is the best solution to this problem? I've looked for a heat separator online with no luck...is there another name for it?
 

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It's called a phenolic spacer. They're usually some non-heat-conducting material.
 

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It's called "fuel percolation" which occurs when the temperature of the fuel in the float bowl increases enough to cause the lighter compounds (especially ethanol) to vaporize and bubble the fuel into the carburetor throat. Quality of fuel is one factor. Underhood temperatures is another. Heat transfer from the intake manifold to the carburetor is yet another. Addressing these is the solution.

Better quality fuel, lowering underhood temps by reducing engine heat output (more spark advance, richer mixture) or venting more hot air from under the hood and a phenolic spacer are all useful methods. Another contributor is rubber fuel line between the pump and carburetor. Rubber insulates the fuel from the air passing by the line, but absorbs the heat and passes it on. Steel line lets the fuel give up heat.
 

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I have the 2 barrel motorcraft 2100. I think I'm going to do a combination of a hood scoop and the heat separator. I already use 89 octane gas and it is my daily driver so I don't want to put the even more expensive fuel in.

Btw thank you for the quick responses. I am new to this forum and was not expecting this much feedback.
 

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351C

Caleb, don't worry about if there is ethanol in your fuel or not. Avoiding ethanol, even if possible in your area,alone won't cure your problem. Does your car have vacuum advance ? If so, how is it hooked up, manifold or ported ? LSG
 

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Caleb, don't worry about if there is ethanol in your fuel or not. Avoiding ethanol, even if possible in your area,alone won't cure your problem. Does your car have vacuum advance ? If so, how is it hooked up, manifold or ported ? LSG
Did anyone suggest it would?

Allen
 

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yes, you

AllenTurn, yeah, YOU. 'check for non-ethanol gas'. Bart said ethanol might be in his fuel and evaporating. Ethanol is one of the lighter compounds. But fuel WITHOUT ethanol has OTHER light compounds that will also easily evaporate. Bart knew this. YOU'RE the one who suggested avoiding ethanol. LSG
 
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